Assessment of Radiation Exposure and Radioactivity from the Liquid Discharge in a Nuclear Medicine Facility

Abstract

Aim: Radionuclide imaging and therapies produce radioactive liquid waste that may lead to significant radiation exposure to the general public. The study aims to assess the radiation exposure rate to public sewerage from a modified delay tank facility. We shall also evaluate the exposure rates and overall radioactivity at several points.

Materials and methods: After having appropriate permission from the AERB, we measured the radiation exposure from the radionuclide therapy ward. Ward has three isolation beds and a single delay and decay tank of a capacity of 7500 liters. Effluents from the delay tank are processed at the filtration plant of the institute and subsequently released in the public sewerage. We obtained samples from several sites to determine discharged radioactivity.

Results: A total of 38 patients received 129.4 ± 42 mCi (Range 40- 200) radioiodine therapy during the study. Discharge of the tanks was done two times during the study. The radioactivity discharges into aeration plant were 89.2 and 71.2 mCi that correspond to 440.05 and 351 MBq/m3, respectively. This was diluted by the aeration tank (6 million liters). Finally, at the discharge time, the radioactivity in the discharge was 1.6 and 1.5 MBq/m3, respectively. The highest exposure rates were 14 μSv/h near the delay tank, which rapidly decreased on moving to the surrounding.

Conclusion: Our study indicates that the addition of the dilution method and close monitoring may significantly reduce the radiation exposure and overall radioactivity release from the facility. Old facilities that do not have space to add up the tank capacity may get a benefit from it. A small change in the practice, such as admitting patients alternate months or providing extra decay time for radioactive waste, may lead to a cost-effective alternative.

Keywords: Delay tank; survey meter; well counter.

Figure 1

Delay tank layout for 131I isolation ward as per the National Regulatory Body guidelines

Figure 2

Diagram showing the existing isolation ward and delay tank facility

Figure 3

Systematic diagram showing the treatment of the radioactive waste released from the nuclear medicine isolation ward before draining into the public sewerage system

Figure 4

Primary y-axis (bar chart) showing activities in mCi from both months (every week and at the time of discharge). Secondary y-axis (line chart) showing corresponding radiation exposures

Figure 5

The bar chart represents radiation exposure levels at the various sites in the delay tank and dilution tank facility